Not Applicable.
1. Field of the Invention
The instant invention most generally relates to spectrometers and spectral instruments. Particularly this invention relates to the manipulating and the directing of electromagnetic beams, preferably within the optical spectrum. More particularly, using appropriate optical elements, a plurality of non-interfering beams paths are created and each of which beams are controlled, directed as to the paths, and shaped, dispersed, diffracted and otherwise manipulated. The manipulation, directing, redirecting, diffracting, frequency selection and the like, accomplished to each of the beams of the plurality of beams is accomplished by some of the same elements. More particularly, there are two beams, a first or an in beam and a second or an out beam going in substantially opposing directions and passing through the same control, manipulation and direction elements concurrently and without interference. One beam manipulating element is a means for diffraction which diffracts or spatially separates the wavelengths within the spectrum of each of the beams concurrently and without interference with gains in the discrimination of the wavelength from the spectrum. The preferred means for diffraction is a concave spherical shaped grating with a specially configured hyperbolic shaped holographic grating surface designed to diffract and reflect the beam off of the optical axis of the grating structure. Even more particularly, the invention is a spectral instrument which combines the functions of several optical instruments usually used separately in spectrometry measurements. The instrument may have any combination of elements such as means for coupling a beam to be measured into the instrument, a monochromator which monochromator preferably has the dual and non-interfering optical beam paths, means for scanning the optical spectrum, such as a motor and drive mechanism which causes the means for diffracting to move through an arc and consequently discriminate a particular set of wavelengths, means for sorting out harmonics or orders of the monochromatic beam, such as filters, means for chopping or modulating the beam being measured, means for detection of the selected frequency/wavelength and means for amplification of the power level of the detected wavelength. Most particularly, the invention is a spectral system which includes the spectral instrument and which may have at least a power module and one or a combination of such as a means for remotely controlling the scanning, the filtering/sorting functions and the control of the power to the instrument. The instrument may preferably have a housing or casing, within which the optical elements of the instrument are housed, which housing protects the contents from changes in or unwanted characteristics in ambient conditions including spatial orientation, atmosphere and mechanical shock. The operation of the preferred system and the instrument requires no adjustments or manipulations by an operator or user. Scanning, order sorting and the measured output of the instrument are all controllable and available to the user from a PC (Personal Computer). Access to the instrument, using the system may be by remote connection such as by telephone lines via a modem or by any form of dedicated communication with the instrument.
2. Description of Related Art
A spectrometer is an instrument which is used in the analysis of the characteristics of electromagnetic energy over a certain identified spectrum or frequency distribution. The frequencies normally considered to be in the spectrum have wavelengths from as long as 10,000 nanometers (nm) to as short as 100 nm all of which frequencies are within the spectrum of the optical portion of the electromagnetic spectrum. The instrument may be used for any combination of functions such as observing, resolving, recording and amplitude measuring of frequency distribution and the amplitudes or power levels of the various frequencies or wavelengths which make up the spectra of the observed optical spectrum. A spectroradiometer is a spectrometer that is more specifically equipped with scales for measuring the positions of spectral lines of radiation and the level of energy of each of the wavelengths which relate to the spectral lines. A spectrophotometer is used for measuring the intensity of a particular spectrum in comparison to the intensity of light from a standard spectral source to determine the concentration and the composition of the substance that emits or absorbs spectral lines of the spectrum.
Currently, a spectrometer that performs spectrometry, spectroradiometry, and spectrophotometry is a large, immobile device, not amenable to mobile applications. The current practice is to assemble individual components such as input optics, at least one monochromator, filters to eliminate unwanted harmonics or orders, detectors and amplifiers. That is, if one wishes to do a spectroradiometric measurement of a particular optical beam, the individual components are carefully selected and positioned in order to carry out the radiometric measurements. In addition, many of these currently-available devices do not have the resolution nor the precision to accomplish the many tasks for which a spectrometer could be useful. One common problem is inadequate stray light rejection. Stray light rejection, which is express as a xe2x80x9cscatter figurexe2x80x9d, is the ability of the system to measure only light of a specified wavelength and to ignore all other light. Other issues with currently-available spectrometers, which issues are considered to be of disadvantage or inconvenience, include complex operating procedures, frequent recalibration requirements, and the oxidation of the optics. Most spectroscopy systems which are reasonably priced and which are relatively easy to use do not provide for accurate and stable measurements. There are many polychromator systems that are reasonably affordable however, the scatter rejection is inadequate thereby making it difficult to obtain absolute measurements that represent true and accurate readings of the character of the spectrum. Purity (scatter) in the current technology often causes gross errors in the readings. In fact, the scatter figure for some current systems is not good enough for accurate measurements of modest signals from broadband sources. Other inexpensive systems fall short when it comes to high resolution, wide band coverage, small signal amplification, and order sorting.
U.S. Pat. No. 4,867,563 in class 356/328 discloses a silicon photodiode for receiving light: (1) having a bandwidth in the range of between 2 and 15 nm (nanometers) from a pivotable concave holographic diffraction grating within the wavelength range of between 250 and 1150 nm at a scanning rate in the range of 20 to 100 nm per second; (2) having stray light of high intensity and undesired frequencies and the shorter wavelength harmonics of the selected frequency range blocked by filters; and (3) having flux of at least 10 microwatts per square meter of diffuser plate for each nanometer of bandwidth. Automatic electrical zeroing is obtained by blocking all light at the beginning of each scan, obtaining an electrical drift-related signal and using the drift signal to adjust the measured signal during the scan. Several different sensing interfaces can be used, including a quartz, light fiber probe having at least a 50% packing density and a cone angle of at least 24 degrees. The data and the programming storage are at least 30 K bytes but the instrument uses relatively little power when the instrument is not scanning. The purpose of this invention defined in the ""563 Patent is to provide sufficient sensitivity, spectral resolution and speed for environmental measurements in the field using a portable spectroradiometer.
U.S. Pat. No. 5,528,364 discloses a monochromator which employs a spherical mirror, a traveling plane mirror with simultaneous rotation, and a varied spacing plane grating. The divergent beam from the entrance slit is converged by the spherical mirror located at the various positions in the monochromator depending of the inventive system. To provide the meaningful diffraction efficiencies and to reduce unwanted higher order lights, the deviation angle subtending the incidence and diffraction beams for the plane grating is varied with the position of the traveling plane mirror with simultaneous rotation located in the front or back of the plane grating with wavelength scanning. The outgoing beam from the monochromator goes through the fixed exit slit and has the same beam direction regardless of the scanning wavelength. The combination of properly designed motions of the plane mirror and novel varied-spacing parameters of the inventive plane grating corrects the aberrations and focuses the monochromatic spectral image on the exit slit, enabling measurements at high spectral resolution.
In the invention defined in the ""364 Patent, the centers of the entrance slit, spherical mirror, traveling plane mirror with simultaneous rotation, grating, and exit slit lie in one and the same vertical plane. A spherical mirror accepts the beam from the entrance slit at an angle of incidence xc3xa8 and produces a vertically converging beam incident onto a varied spacing plane grating. Vertically diffracted light of wavelength e is focused on the exit slit and can also be focused horizontally if an optional concave mirror is inserted. Wavelength scanning is carried out by grating rotation about the central groove while the mirror is traveling on the normal to the exit slit and rotating. Therefore the deviation angle of the grating varies with the scanning wavelength. As the role of the plane mirror is merely to transmit the diffracted rays to the exit slit at an angle xc3x6, the system is considered as a double-element system consisting of the mirror and the grating. Thus, the design of this monochromator is determined by the ruling parameters of the grating, the total distance the light travels and the deviation angle for given values of the wavelength scanning range.
U.S. Pat. No. 5,394,237 in class 356/328 discloses a lightweight, portable spectroradiometer that provides a real-time data acquisition capability from 0.3 xcexcm to 3.0 xcexcm with selectable integration periods, and operates through a Centronics parallel port of a personal computer to program the spectrometer, store data, and to provide real time graphic output. Equipped with two spectrometers operating from a common optical input, high detector efficiency is obtained by structuring the detector elements for maximum energy gathering capability, matched to slit aperture size and orientation. No filters or mechanically driven mirrors are required, thereby permitting a compact, easily portable instrument. If desired, the detector array is readily adaptable to thermoelectric cooling.
U.S. Pat. No. 5,646,735 in class 356/402 discloses a hand-held instrument for reflection measuring of optical density and color on printed sheets used not only for measuring light reflections but also for transmission of the test data to a computer. The hand-held instrument is provided with an instrument housing having a measuring head and an electronic control unit in the housing for converting the values measured in the measuring plane of the sheet. The housing contains an electronic computer input system connected to the electronic control unit, at least one click knob operable externally on the housing, and a control element for the inputs to the computer input system. A junction box is provided for an interface for transmission of the measured data converted in the electronic control unit into signals to a computer.
The patents noted herein provide considerable information regarding the developments that have taken place in this field of spectrometry. Clearly the instant invention provides many advantages over the prior art inventions noted above. Again, it is noted that none of the prior art meets the objects of the disclosed spectrometer, the special grating structure and the spectral measurement system in a manner like that of the instant invention. None of them is as effective and as efficient as the disclosed spectrometer for high performance, compact size, ease of use, versatility, and high precision.
The invention can most generally be characterized as a spectrometer, i.e., as a spectral instrument using multiple non-interfering optical beam paths and special optical elements. The special optical elements for use with the instrument are used for directing the optical beam and/or altering the form of the beam. The instrument has the potential, depending upon the totality of the optical components incorporated into the instrument, to be a monochromator, a spectroradiometer, a spectrophotometer and a spectral source.
The spectral instrument may further be a part of the spectral system of the invention. The system may include the spectral instrument, a power module and means for remote control of the instrument. Such remote control may be by use of a personal computer or a control system dedicated to the control, measurement and analysis of the collected information.
The multiple non-interfering beam paths are created using specially designed optical elements. Without these elements, the instrument could not function in the manner described. The specially designed optical elements or components are such as a diffraction grating, a splitter box used to direct an entrance or incoming beam as well as an exit or return beam, a zero back-lash drive system for causing the movement of the grating element, an orientation of and a physical/spatial relationship between the field lenses, slits, return mirror, reflecting prism, relay or turning lens, all of which define the multiple paths for the traverse of the incoming optical energy. Preferably, there are two defined paths each of which use some of the same beam directing and beam altering components and each of which path is non-interfering with the other beam path. One of the paths may be characterized as an xe2x80x9cin pathxe2x80x9d and the other an xe2x80x9cout pathxe2x80x9d.
Particularly, the present invention provides for a double pass through the grating to increase dispersion, reduce scatter while maintaining a perfect temperature-independent spectral match for the second pass. Using the grating twice reduces scatter by about a factor of 1000, increases the dispersion by a factor of two, and eliminates any temperature-related mechanical spectral drift which often is present with two separate monochromators.
One aspect of the invention is a specially designed grating which is moveable through a defined number of degreesxe2x80x94in the preferred embodiment the movement is through about 25 degrees of rotation about an optical axis of the grating component. In part because of the specially designed grating component, the grating can cause the concurrent diffraction of a plurality of incident optical beams, each of which beams have different angles of incidence and different angles of reflection. It is important to note that the path of the incident and the reflected beam to and from the grating is xe2x80x9coff-axisxe2x80x9d. That is, the beams going to and from the grating do not use the optical axis of the grating structure. The grating structure in effect diffracts the incident beam, i.e., spatially separates the incident beam so as to locate the different wavelengths in spatial relationship and reflect this spatial spectrum in a predetermined direction. A portion of the spatial spectrum, i.e., the diffracted beam, impinges on a slit which selects that wavelength which is incident to the slit. The portion of the spatial spectrum impinging on the slit and consequently the frequency/wavelength of the optical signal which is selected, is a function of the moveable position of the grating structure. Use of this grating structure concurrently by more than one non-interfering beam of spectral energy has many advantages over the sequential use of separate monochromators.
Another aspect of the invention is the particular orientation and location of optical elements to direct and define a plurality of paths for an optical beam and alter the optical beams of energy which enter the instrument. The optical elements directing and altering the beam define the paths and are used concurrently and simultaneously and in a non-interfering manner to direct and alter the form of the energy contained in each of the beams and in the beam paths. The optical beam paths in the preferred embodiment, are in directions which are non-interfering and basically opposed each to the other. Energy within the optical spectrum of each of the beam paths is simultaneously acted upon by the same elements.
Yet another aspect of the invention is to provide a means for automatically initializing the instrument using a source of known wavelength and also for verifying the accuracy of the measured characteristics of the incoming optical beam. In the verification and initialization modes, the known wavelength is dispersed by the grating but the energy beam is, this time, xe2x80x9con-axisxe2x80x9d that is, it is on the optical axis of the diffraction grating element. A detector or receiver of the known signal dispersed on-axis from the grating surface is measured by the calibrated and known receiver which can then be compared with the dispersed incoming signal. The position of the stepper motor, worm gear drive system which provides the angular movement of the grating is automatically positioned so that the calibration wavelength is caused to be over the first discriminator slit of the instrument.
It is therefore an object of the present invention to provide a spectrometer system, having as a part of the system a spectral instrument wherein the spectral instrument comprises means for detecting optical wavelength energy; means for performing functions upon detected optical energy the functions performed being those of typical and known spectral instruments such as monochromators, spectroradiometers, spectrophotometers and a spectral energy sources. An additional component of the system is at least a power module which provides to the instrument, operating power, means for communicating, means for interconnecting the spectral instrument with a computer or other means for controlling the instrument as to the performance of the functions. The system may also have such features and components as means for receiving commands from a list of commands and means for responding to each of the commands. The commands consist of at least one command selected from the group consisting of power on and off, scan wavelengths including selection of start wavelength and end wavelength, read and display measured data, instrument calibration and validation, and a command to cage a drive mechanism. The drive mechanism causes an arcuate movement of a grating component which movement effectively causes the scanning of the spectrum of the optical energy into the instrument. There may also be provided as a part of the system, software which is operable on a computer used to control and communicate with the system. The software provides means for remotely accessing, controlling functions, controlling performance, and controlling measurement and characterizing of measured data developed by the spectral instrument. Other features incorporateable into the system is programmable electronics and means to indicate malfunction within the instrument such as at least one indicator light.
Another object of the present invention is to provide the spectral instrument with a plurality of optical components. Each optical component is particularly oriented and located each with respect to the others. Some selected optical components function to direct and define a plurality of beam paths for an optical beam and other selected optical components function to alter the nature of the optical beams as to energy dispersing the spectrum and discriminating wavelengths from the spectrum of wavelengths which enter the spectral instrument. Each of the beam paths are used concurrently and simultaneously and in a non-interfering manner by any optical beam traveling over the beam paths.
Yet another object of the present invention is to provide a spectral instrument for performing analysis of spectral energy of an input optical beam in terms of the unique paths taken by the input optical beam which paths are defined by a plurality of optical components. The input optical beam may have a particular wavelength distribution and energy distribution. The basic form of the spectral instrument comprises; a first monochromator portion comprising a first entrance slit. This first entrance slit is in optical beam path relationship with a grating component. There is also a first exit slit which is in diffracted and wavelength selected beam path relationship with a first reflective surface of the grating component. And there is a second monochromator portion comprising a second entrance slit. The second entrance slit is in a mirror image optical beam path relationship with a return mirror and with the grating component. A second (2) exit slit is in twice diffracted and twice wavelength selected beam path relationship with a second reflective surface of the grating component. The optical beam paths of the first monochromator portion and the second monochromator portion are so configured and designed so that each path, that is the path taken by an optical beam through the first monochromator portion is substantially non-interfering with the path taken by the optical beam through the second monochromator portion.
A still yet another object of the invention is to provide additional features to the instrument all directed toward enhancing the performance and to increase the functions the instrument can perform. For example there may be a means for chopping at a predetermined chop rate, any optical beam within both monochromator portions. The means for chopping is preferably positioned in optical beam path relationship with the first exit slit and a return mirror and the return mirror and the second entrance slit. So the spectral instrument may scan the spectrum, there is provided a drive mechanism which provides the means for moving the grating component thereby selecting the wavelength discriminated by both the first monochromator and the second monochromator.
A further object of the present invention is to provide a spectral instrument for performing analysis of spectral energy of an input optical beam in terms of a plurality of optical components and the functions performed and positional relationships of the components. The spectral instrument comprises; a first entrance slit upon which an entrance optical beam, derived from the input optical beam, is directed in a first path (1). The first entrance slit creates an entrance slit beam which has a cross section dimensions substantially equal to the cross section dimensions of the first entrance slit. There is a first location on a prism first reflecting surface upon which the first entrance slit beam is directed in a second path (2). The prism first reflecting surface directs the first entrance slit beam on a third path (3) to a grating component. The first entrance slit beam is thereby diffracted by the grating component creating a first diffracted beam which first diffracted beam is reflected in a fourth path (4) from the grating component surface to a first location on a prism second reflecting surface. A field lens upon which the first diffracted beam is directed on a fifth path (5) from the prism second reflecting surface focuses and directs the first diffracted beam and a defined and selected portion of the optical spectrum of the first diffracted beam onto a first exit slit. The first exit slit thereby discriminates and produces a narrow bandwidth beam of optical wavelengths. A return mirror, upon which the narrow bandwidth beam is directed on a sixth (6) path, creates a mirror image beam of the narrow bandwidth beam and directs this beam on a seventh path (7) back to the field lens. A second entrance slit, upon which the mirror image beam is directed on an eighth path (8) by the field lens, provides further discrimination of the mirror image beam. A second location of the prism second reflecting surface is where the discriminated mirror image beam is directed. From this second location the discriminated mirror image beam is directed on a ninth path (9) to the grating component. This mirror image beam is again diffracted or dispersed by the grating component creating a diffracted discriminated mirror image beam which is reflected on a tenth (10) path from the grating component surface to a second location on the prism first reflecting surface. There is a second exit slit upon which the second location on the prism first reflecting surface directs the diffracted discriminated mirror image beam providing a second discrimination of the diffracted mirror image beam.
A yet further object of the invention is to provide additional features to the instrument all directed toward enhancing the performance and to increase the functions the instrument can perform. For example there may be a means for chopping at a predetermined chop rate, any optical beam within the spectral instrument. The means for chopping is preferably positioned in the path of the first diffracted beam and the mirror image beam. So the spectral instrument may scan the spectrum, there is provided a drive mechanism which provides the means for moving the grating component thereby selecting the wavelength thereby selecting the wavelength discriminated by both said first exit slit and said second exit. A turning mirror directs therefrom, the diffracted discriminated mirror image beam into an instrument output portion wherein may be located an order sorting filter followed in the path by a detector and perhaps a detector amplifier preferably a lock-in or phase locked amplifier. There may also be input optics, which input optics is selected from such as a wide angle lens, a narrow angle lens and fiber optics. And there may be means for optical initialization and a means for verification of wavelength using, on-axis, the grating component and a known wavelength source.
The drive system or drive mechanism is a specially designed anti-backlash system using a stepper motor coupled to a slip-coupled magnetic system and then to a flexible shaft having a worm gear engaging a sector drive component which in turn cause movement of the grating assembly. The worm gear and the gears on the sector drive are configured to substantially eliminate any back-lash at the gear engaging location.
These and further objects of the present invention will become apparent to those skilled in the art to which this invention pertains and after a study of the present disclosure of the invention.